Magento

Magento is an open source e-commerce web application. Magento Community Edition can be downloaded for free. Developers can modify the core code and add features and functionality by installing extensions from the Magento Connect marketplace.

Sphinx

Sphinx is an open source full text search server, designed from the ground up with performance, relevance (aka search quality), and integration simplicity in mind.

Sphinx lets you either batch index and search data stored in an SQL database, NoSQL storage, or just files quickly and easily — or index and search data on the fly, working with Sphinx pretty much as with a database server.
A variety of text processing features enable fine-tuning Sphinx for your particular application requirements, and a number of relevance functions ensures you can tweak search quality as well.

Revive Adserver

Revive Adserver is a free open source ad serving system that enables publishers, ad networks and advertisers to:

Serve ads on websites, in apps, and in video players, and collect detailed statistics about impressions, clicks and conversions

Manage campaigns for multiple advertisers and from ad networks all at once, via an easy to use interface

Track and report campaign performance, including click-through rates, conversion rates, revenue, eCPM and conversion details, like basket value and number of items purchased

Joomla!

Joomla is an award-winning content management system (CMS), which enables you to build Web sites and powerful online applications. Many aspects, including its ease-of-use and extensibility, have made Joomla the most popular Web site software available.

Best of all, Joomla is an open source solution that is freely available to everyone.

Drupal

Drupal is an open source content management platform powering millions of websites and applications. It’s built, used, and supported by an active and diverse community of people around the world.

WordPress

WordPress is a free and open source blogging tool and a content management system (CMS) based on PHP and MySQL which runs on a Web hosting service. It has many features including a plug-in architecture and a template system.

TYРOЗ

TYPO3 is an enterprise-class, Open Source CMS (Content Management System), used internationally to build and manage websites of all types, from small sites for non-profits to multilingual enterprise solutions for large corporations.